In the past two years, I have received several reports of fields suffering yield loses due to stem rot. Last year I saw several affected fields. This year, I am starting to get reports of fields being affected. I visited one such field last week.
After the water was drained, plants in the affected area seemed to burn down and dry much quicker than the rest of the field. Much of the rice was down.
Inspection of the tillers showed outer lesions that were already dry. However, when cutting open the tillers, the inner sheaths and main culms were rotted. In some cases, mycelium and sclerotia, the resting state of the fungus, could be seen growing inside of the culm. Most panicles were partially filled. This field most likely will suffer a yield loss.
Stem rot infections start at the water line. Surviving sclerotia from previous seasons float to the surface of the water and infect plants during tillering when conditions are favorable. Infected young tillers may die; later infections on older tillers can reduce panicle size and grain quality, and increase lodging.
Management of this disease should incorporate several tactics, probably the most important is residue management. The severity of this disease has been shown to be related to the amount of inoculum present in the field. As the number of viable sclerotia in the seedbed at the beginning of the season increases, the severity of the disease late in the season increases. Straw burning is the most effective way to reduce the amount of inoculum in the field, but is not always feasible. Experiments have shown that sclerotia survive better if they are inside plant tissue, therefore chopping and incorporating the residue to promote decomposition can help reduce the amount of inoculum. If baling, cutting the straw as close to the ground as possible will remove inoculum from the field.
Nitrogen has been shown to affect stem rot. Excess levels of N can increase stem rot severity. In fields with stem rot problems, adjusting the N rate can help reduce the impact of the disease.
Fungicide trials conducted in 2012 and 2013 seem to indicate that currently registered fungicides have an effect on stem rot incidence and severity. Further trials are being conducted this year to confirm those results./table>
I was evaluating armyworm injury in plots and noticed there was quite a bit of panicle blanking not caused by armyworms. When armyworms injury panicles, they feed on the rachis of panicle branches, causing those branches to dry out. Sometimes the kernels in those branches may be partially filled, but since they stop receiving nutrients and water due to the biting injury of the armyworm, they dry and turn straw colored. Most of the time, the branches brake off at the point of injury and can be seen hanging on the panicle. If you look closely at where the rachis is broken, you can see the biting mark of the armyworm.
The other blanking I was noticing was a little different. It was mostly on the panicles under the canopy, although some could be seen in the panicles on top. Blanked branches turned white, almost as if bleached, and kind of translucent. This might be because these panicles were young. Most likely they will dry out and also turn straw color. None of these injured branches were hanging on the panicle and no biting marks could be noticed. I suspect this blanking was caused by high temperatures. Temperatures above 104 F during flowering dry the germinating pollen tube before fertilization and cause blanking. It seemed that some areas in the field were more affected than others.
Going back to armyworms, I found very little injury in my Butte County trial. Two trials in Colusa had no injury. The number of armyworm moths caught in the traps as of 8/24 have come down again. I suspect we won't see the numbers climb up again, therefore the risk of armyworm injury now is very low.
Click on the images below to see a close up of armyworm injury (left) and high temperature blanking (right).
- Author: Whitney Brim-DeForest
The 2nd Annual Rice Weed Course will take place:
Friday, September 15, 2017
from 8:30AM to 4:25PM (Registration begins at 7:30AM)
Hamilton Road Field (on West Hamilton Rd. between Hwy. 99 & Riceton Hwy.)
and Rice Experiment Station, Biggs, CA
The day will begin with an interactive tour of the Weed Science research plots at Hamilton Road. Participants will also spend time learning about weed identification for important rice weeds both at emergence and at heading (including identification of weedy rice).Presentations will cover herbicide resistance management and the latest information on weedy red rice. Attendees will also hear an update about rice pesticides in California. This course is a great opportunity to interact directly with the UCCE and UC Davis Rice Weed Research Team!
For a full agenda and registration go to:
For questions, please contact Whitney Brim-DeForest at 530-822-7515, or by email at email@example.com
Credits for PCA, QAC, QAL, Private Applicator, and CA Certified Crop Adviser are pending.
For two years in a row I have received a report from a PCA in Yuba County of conchuela stink bugs on rice. This is very unusual; I have never seen these stink bugs on rice before, and I'm not very familiar with them. A quick on-line search shows that they are common on the western US; they can be a pest of cotton, alfalfa seed and sorghum, but it has a wide host range. Our UC IPM webiste only lists them as a pest of apple and pear, so I don't know how prevalent they are in agronomic crops in the Sacramento Valley.
Last year they did not affect yield or quality in the field where they were detected. I am not considering these bugs a pest; just incidental at this point. I'd love to hear from other PCAs or growers if they have noticed them in their rice.
Every year we see some off-types in our public varieties that have a genetic mutation we call elongated upper internode. This mutation causes the internode below the panicle to elongate, resulting in panicles that stick above the canopy. Some have confused this abnormality with weedy rice.
It seems that the occurrence of this abnormality may be related to weather - some years we see it more often than others. In any case, the frequency with which it occurs is so low that it does not affect yield.